How will the old bridge be removed?
Crews with Total Construction began the removal process by taking down the west approach to the old bridge when the new bridge opened the beginning of August. The removal process of the main trusses will begin by incrementally removing the bridge deck, deck stringers, sidewalk and railings before dropping the remaining truss sections into the river.
The proposed details for removal of the bridge include:
1. Removal of the west end approach which has been completed over the past few weeks.
2. Removal of the existing concrete deck is progressing from west to east across the bridge. The contractor plans to remove the deck in sections. These sections will be pushed over to the east side to be processed. Plans include recycling the concrete and steel.
3. Each of the three trusses will be removed by using small charges or explosives to break it up into sections. The west truss section will be removed on the first blast. Sometime later, the other trusses will be removed. Cranes and barges will be used to remove the sections from the main river channel.
4. Crews will use cutting torches to pre-cut select locations on each of the three spans of the bridge. Hundreds of these cuts will be made in each span. At each of the pre-cut locations made by cutting torches, small incendiary devices called “shaped charges” will be placed to make the final cut. All charges will be set off simultaneously to drop each span. These charges will separate each span up to 30 individual pieces.
5. When it is time to take down the middle truss section of the bridge, a temporary causeway will be built for the cranes removing the pieces.
6. The piers will be removed to a depth of 1613 feet or lower. It is several feet below the existing river bed as it is today and will not be an obstacle to boats. This depth was established by the U.S. Coast Guard as a safe navigable depth.
7. Any debris from the demolition work will be removed from the river and the project site as per guidance from the US Coast Guard and US Army Corps of Engineer. Sonar sweeps will be made before and after the demolition work. Divers, long reach backhoes and even hand picking will be utilized.
I heard a large piece of equipment called a King Kong was used on the bridge. Why?
Remember as a child wearing rubber overshoes and walking through deep mud when all of a sudden the suction of the mud has grabbed your boot and you step out of it, leaving your boot behind? You turned back and tugged and pulled to free your boot from the mud. That’s an elementary example of the kind of set up and adhesion that occurred when sheet piling at pier 10 on Liberty Memorial Bridge was driven for the cofferdam.
A pile driving hammer drove in the piling for the cofferdam. While the sheet pile was driven, water and soil was forced away from the sheet. When pile driving stopped, the water and soil rushed back in causing set up and adhesion to the cofferdam sheet pile. Early testing before the job was started identified soil types using procedures that followed standard engineering practices. Determining adhesion qualities of the soil are not part of those procedures. The soil testing and identification of soil types for this project met all engineering standards.
Just like the extra work required to free your boot from the mud, it requires extra work to remove the sheet piling. That’s why a larger vibratory hammer was rented to extract the sheet piling. It is a post-construction task, one that takes place after construction of the piers inside the cofferdam is finished. It does not affect the structural integrity of the completed piers.
However, there could be some positive effects to the structural integrity of the bridge due to the soil type that adhered to the piling. That’s because the support piling on which pier 10 is built is in the same soil that stuck the cofferdam sheet piling, providing a strong support. Since the support piling for the pier reached that same level of soil, it saved time and money -- the support piling did not have to be driven as deeply as originally planned in order to support pier 10.
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When will the existing bridge be demolished?
In late summer of 2008, when two full lanes of the new bridge are completed, traffic will be transferred from the old bridge to the new bridge. The old bridge will be removed and the final two lanes of the west approach bridge will be tied to the new river bridge.
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Will the old bridge be blown up like the Four Bears Bridge was?
It’s uncertain at this time. The contractor has not submitted plans for demolishing the old bridge.
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In the beginning, there was talk of parks under the new bridge, are those still part of the plan? What will they be like?
Since the beginning of planning the new bridge design, when the Citizens Advisory Committee and the Technical Advisory Committee met, it was apparent that people in both Bismarck and Mandan like their parks and their recreation trails. So, parks have been planned for both sides of the river. In the fall of 2007 a technical advisory group has been looking at several options for the plans and it is anticipated that public hearings before spring 2008 will help shape the plans for the parks
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Since the collapse of the 35W bridge in Minneapolis, has the DOT added inspectors to the Memorial Bridge project?
No new inspectors have been added to the construction project. Since the beginning, there have been nine DOT inspectors on the job assuring quality of the project
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Do the lower water levels of the Missouri River make it easier to build the bridge?
Not necessarily. The lower water levels make it difficult to maneuver the barges with cranes and materials.
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There was some talk about missing pieces of concrete on the surface of the pier on the Mandan side of the river, what happened and how does it affect the structural soundness of the bridge?
When workers discovered hollow-sounding areas while finishing the surfaces of the pier 7, the North Dakota Department of Transportation (NDDOT) ordered further investigation and found the exterior two to six inches in some spots of the pier had separated from the rest of the structure. This separation is called “delamination” and it does not affect the structure of the pier. It is a cosmetic issue that requires grouting to repair the appearance of the spot.
NDDOT engineers have evaluated different grout materials submitted by the contractor to find what will work best for the delaminated areas on pier 7. Once steel girders are set overhead at pier 7, finishers will return to grout the surface of the pier in the spring. NDDOT is committed to not only designing and building a solid and safe Liberty Memorial Bridge, but one that is also aesthetically appealing.
The delamination does not pose a structural problem to the bridge, but rather a cosmetic situation. That’s why crews will blend in the problem areas to the rest of the face of the pier.
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Where
can I watch the construction?
Areas near the construction site are
private residences and there is no public access to these residential
areas. On the west side, along Marina Road and Pirates Loop, the
public can look through the perimeter safety fence to view work
in the staging yard and the west end of the new bridge. On the east
side, construction is visible from Shelter 11 at Sertoma Park and
the nearby volleyball courts.
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Why is the
south sidewalk closed?
Construction on the east end of the
bridge prevents safe access to the south sidewalk.
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Will the north
sidewalk be closed?
Eventually, when construction prevents
access, there will be no safe way to continue pedestrian traffic
to the west. The intent right now is to keep the north sidewalk
open as long as possible.
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When will
the project be complete?
In the summer of 2008, traffic will
be switched to the new bridge. The old bridge will be demolished
late in 2008 or early 2009. The parks and memorial areas will be
complete in 2008 and 2009.
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What is
being done to preserve the history of the old bridge?
The North Dakota Department of Transportation
Cultural Resources Section along with the State Historical Society
of North Dakota have researched the history of the old bridge, collected
old photographs and archived them. This information is being integrated
into a Traveling Exhibit and school Send Trunk on truss bridges
which should be available from the State Historical Society some
time in 2007. Detailed documentation on the bridge has been completed
(Historic American Engineering Record [HAER]) and is available through
the Library of Congress. Microfilm copies of HAER documentation
are available at over 110 libraries across the country. The Memorial
Bridge is also being interpreted for the public as part of the parks
and memorial areas to be completed after construction of the new
bridge, in a documentary on historic bridges in North Dakota, and
in a book being produced on the historic and memorable bridges of
North Dakota.
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